Burner assembly having a tertiary air nozzle

ABSTRACT

A burner assembly for mounting adjacent an opening in the wall of a furnace, including at least one fuel burner member disposed in a sleeve having an end portion terminating adjacent the opening. A first supply of combustion air for the fuel is directed from a location external of the sleeve toward the opening and a second supply of combustion air is introduced into the sleeve. A cup shaped insert is disposed in the sleeve for defining a nozzle having an annular discharge opening for discharging the second supply of air towards the stream of fuel discharging from the burner member.

United States Patent Grozegno et al.

BURNER ASSEMBLY HAVING A TERTIARY AIR NOZZLE Inventors: Walter P. Grozegno, Florham Park;

Norman K. Trozzi, W. Caldwell, both of NJ.

Foster Wheeler Corporation, Livingston, NJ.

Filed: July 5, 1974 App]. No.: 486,254

Assignee:

U.S. CI. 431/184 Int. Cl. F23M 9/00 Field of Search 431/181, 182, 183, 184,

3,7l5,l8l 2/1973 Zink et al. 43l/l84 Primary Examiner-Edward G. Favors Attorney, Agent, or Firm-Marvin A. Naigur, Esq.;

John E. Wilson, Esq.; Warren B. Kice, Esq.

[57] ABSTRACT A burner assembly for mounting adjacent an opening in the wall of a furnace, including at least one fuel burner member disposed in a sleeve having an end portion terminating adjacent the opening. A first supply of combustion air for the fuel is directed from a location external of the sleeve toward the opening and a second supply of combustion air is introduced into the sleeve. A cup shaped insert is disposed in the sleeve for defining a nozzle having an annular discharge opening for discharging the second supply of air towards the stream of fuel discharging from the burner member.

9 Claims, 3 Drawing Figures PATENTEI] JULZQIQYS 3, 8,97, 199

FIG.

BURNER ASSEMBLY HAVING A TERTIARY AIR NOZZLE BACKGROUND OF THE INVENTION This invention relates to a burner assembly for use in a furnace or the like and, more particularly, to such an assembly in which two separate supplies of combustion air are directed toward the fuel stream discharging from a burner member.

In accordance with conventional designs of burner assemblies associated with relatively large installations such as the furnace portion of a vapor generator or the like, combustion air for the burner is discharged from a windbox towards the combustion zone, which is usually located in, or immediately adjacent to, an opening in the furnace wall. This air is commonly referred to as secondary air and usually comprises all, or at least a very large percentage of the total combustion air requirements for the burner. In some of these arrangements, an additional supply of air, commonly referred to as tertiary air, is introduced through the interior of the burner assembly for discharge towards the combustion zone This tertiary air supplies a relatively low percentage of the complete combustion air requirements for the burner such as, for example, 1 percent.

In these type of designs, a spin is often imparted to the secondary air passing from the windbox towards the opening in the furnace wall in the vicinity of the fuel burner member in order to increase its turbulence and produce a hotter combustion zone. As a result of this spin, a low pressure zone is created in the immediate vicinity of the burner tip to increase flame stability in this area. The tertiary air is normally routed either directly into one end of the sleeve or from a duct connecting the windbox to the sleeve and passes directly through the sleeve to the low pressure zone for aiding combustion in this zone.

However, these designs have proven disadvantageous when applied to installations in which the burner assemblies and their associated components are very large. In particular, as the size of the units increase, relatively large holes or gaps occur in the center of the vortex created by the spinning secondary air, thus causing improper combustion and related problems. Also, with the recent emphasis placed on reducing air pollutants, and especially nitric oxides resulting from the combustion at the burner, some burners have been operated in an off-stoichiometric mode, i.e. with the combustion air delivered to the burners being less than the theoretical amount to support complete combustion, and often as low as 75 percent of this amount. Although reducing the formation of nitric oxides, this type of operation has also resulted in flame pulsations and vibrations, which often cannot be overcome by supplying tertiary air to the combustion zone in the traditional manner discussed above.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a burner assembly for relatively large installa- -tions which can operate at off-stoichiometric conditions while minimizing flame pulsations and vibrations.

It is a further object of the present invention to provide a burner assembly of the above type which includes means efining a nozzle within the sleeve porxri n o'f 'the burner assembly for discharging the tertiary l in a P cular pattern.

It is a still further object of the present invention to provide a burner assembly incorporating a cup-shaped insert cooperating with an outer sleeve to define a discharge nozzle for the tertiary air having an annular discharge opening directed toward the axis of thefuel stream from the burner.

Toward the fulfillment of these and other objects, the burner assembly of the present invention comprises a sleeve having an end portion terminating adjacent said opening, at least one fuel burner member disposed in said sleeve and adapted to discharge a stream of fuel towards said opening, means for introducing a second supply of combustion air for said fuel into said sleeve for discharge from said end portion towards said opening, and means cooperating with said sleeve for directing said second supply of air from said sleeve towards said fuel stream.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view depicting a burner assembly incorporating features of the present invention; and

FIGS. 2 and 3 are enlarged sectional views taken along the lines 2-2 and 33, respectively, of FIG. 1 and incorporating an alternate feature of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The assembly of the present invention will be described in connection with a vapor generator for the purposes of example, with the reference numeral 10 in FIG. 1 of the drawings referring to a fin tube wall which forms a portion of the furnace section of the generator.

A casing wall 12 cooperates with the fin tube wall 10 to define an interior portion 14, it being understood that the latter is bounded by upper and lower walls, as viewed in FIG. 1, to define an enclosure, or windbox, which receives air from a source, such as a fan (not shown), with the direction of the air flow being shown in general by the solid flow arrows in FIG. 1.

An annular refractory collar 16 extends in an opening formed in the fin tube wall 10 with its inner surface being shaped to define a throat portion surrounding a combustion zone 18.

A burner assembly, shown in general by the reference numeral 20, extends through the casing wall 12, with one end of the assembly terminating substantially near the leading end of the collar 16. The burner assembly 20 is supported in a coaxial relationship to the collar 16 by the casing wall 12 and by a register assembly fixed relative to the collar and shown in general by the reference numeral 22. The latter assembly 22 is formed by a pair of spaced plates 24 and 26 having central openings formed therein through which the burner assembly 20 extends. The central opening in the plate 24 is sized so as to support the burner assembly 20 with a minimum clearance, while the central opening in the plate 26 is larger than the outer diameter of the burner assembly to permit air flow, as will be described in detail.

A plurality of vanes 28 are journalled between the two plates 24 and 26 of the register assembly 22 for pivotal movement with respect thereto. Although only two 'vanes 28 are shown in FIG. 1, it is understood that several additional vanes are disposed in a circular relationship around the burner assembly 20. Although not shown in the drawings, it is understood that the angular position of the vanes 28 may be adjustable by cranks or the like, in order to direct the air in a particular path through the register assembly 22 and through the enlarged central opening in the plate 26 to the combustion zone 18.

Referring specifically to FlGS. l-3, the burner assembly comprises an outer tubular sleeve 30 having its leading end portion 30a bent radially inwardly. A plurality of spaced openings 32 are formed through the wall of the sleeve 30 for emitting air from the windbox 14 into the interior of the sleeve. A primary fuel gun, or burner, 34 is supported within the sleeve 30 in a coaxial relationship thereto and is adapted to discharge a stream of fuel towards the combustion zone 18 in a substantially conically shaped discharge pattern as shown by the dashed flow arrows in FIG. 1. A plurality of auxiliary fuel guns, or burners, 36 are disposed in a radially spaced relationship from the gun 34 and extend along a circle as better shown in FIGS. 2 and 3. These guns are for the purpose of discharging another fuel towards the combustion zone 18 which can serve as a primary fuel or as a startup, or auxiliary, fuel. As an example of the types of fuels that can be utilized in the burner assembly of the present invention, oil could be used in the gun 34 as a primary fuel, and gas could be used in the guns 36 for the purpose of burning in conjunction with the oil. Although not shown in the drawings, it is understood that an igniter gun and a flame detector, or scanner, can also be supported in the sleeve 20, for operation in a conventional manner.

A substantially cup-shaped insert 40 is disposed within the leading end portion of the sleeve 30 and includes an inwardly bent wall portion 40a extending slightly divergent to the wall portion 30a of the sleeve 30, to define a discharge nozzle portion having an annular flow and discharge path for the air admitted into the sleeve 30 through the openings 32. A plurality of web portions 42 connect the insert 40 to the gun support sleeve 34a for the purpose of supporting the insert within the sleeve 30.

As better shown in FIG. 3, a plurality of openings 44 extend through the base portion of the insert 40 for allowing a small portion of air entering the interior of the sleeve 30 through the openings 32 to bleed directly to the combustion zone 18.

In operation, the angular position of the vanes 28 may be adjusted to impart a spin to the air passing from the windbox 14 through the register assembly 22 and the opening in the plate 26 to the combustion zone 18. As a result of the spin imparted to the air, a vortex is created in the central portion of the combustion zone to define a low pressure area for the flame resulting from ignition of the fuel discharging from the gun 34. A large percentage of the air passing through the openings 32 into the sleeve 30 passes through the annular discharge opening of the nozzle defined between the cooperating wall portions 30a and 40a of the sleeve and insert 30 and 40, respectively, and towards the central or axial portion of the fuel discharge pattern from the gun 34. The remaining, relatively small, portion of the air passing through the openings 32 into the sleeve 30 passes directly through the openings 44 to the combustion zone 18. It is understood that the design is such that the total supply of tertiary air entering the interior of the sleeve through the openings 32 is relatively high,

such as 10 percent of the total air supplied to the combustion zone 18.

It can be appreciated that in relatively large installations in which the vortex created by the air from the register 22 spinning around the combustion zone 18 is relatively large, that the tertiary air passing through the interior of the sleeve 30 will supply the remaining air needed for optimum combustion. Especially in situations in which the burner assembly is operated in an off-stoichiometric mode, i.e. in which the total air input to the combustion zone 18 is less than the theoretical amount required for complete combustion, the supply of the tertiary air to the combustion zone in the foregoing manner maintains the flame from the combusting fuel from the gun 34 close to its tip and reduces turbulence in the flame envelope, thus preventing flame front pulsations with possible troublesome vibrations. This, in turn, further reduces the formation of pollut ants, primarily in the form of nitric oxides, generated in the flame envelope.

Also, it has been discovered that with the arrangement of the present invention the ignition of the fuel from the gun 34 starts at the outside of the flame envelope in the combustion zone 18 and doesnt burn completely out until the fuel is further out into the furnace. As a result, a longer and more even burning of the fuel is achieved, which further contributes to a lower flame temperature and a reduction of nitric oxides.

According to an alternate feature of the present invention, a plurality of swirl vanes, shown in FlGS. 2 and 3 by the dashed lines and by the reference numerals 50, can be provided to impart a swirling effect to the tertiary air discharging from the nozzle defined between the wall portions 30a and 40a of the sleeve 30 and insert 40, respectively. In this connection, the swirl vanes are disposed between the wall portions 30a and 40a and extend at an acute angle with respect to the axis of the assembly. it has been discovered that the swirling effect imparted to the air as in discharges from the nozzle holds the flame in the combustion zone 18 at the vicinity of the tip of the burner 34 and thus permits the advantages discussed above, yet reduces the total quantity of air that must be supplied to the combustion zone.

It is noted that when operating in the off-stoichiometric mode as discussed above, the remaining air required for complete theoretical combustion can be supplied to the interior of the furnace through overfire ports or idle burner openings, which are not shown in the above drawings.

Of course, variations of the specific construction and arrangement of the burner assembly disclosed above can be made by those skilled in the art without departing from the invention as defined in the appended claims.

What is claimed is:

1. A burner assembly for mounting adjacent an opening in the wall of a furnace, comprising a collar having one end portion extending in said wall opening, another end portion located externally of said furnace, and a through opening communicating with the interior of said furnace, a sleeve disposed externally of said furnace and having an end portion cooperating with said other end portion of said collar to define a first annular flow passage communicating with said collar opening, a substantially cup-shaped insert disposed in said sleeve with the base of said insert disposed inwardly from said end portion of said sleeve and having a plurality of openings extending therethrough, the wall of said insert cooperating with said end portion of said sleeve to define a second annular flow passage communicating with said collar opening, at least one burner member disposed in said sleeve and adapted to discharge a stream of fuel into said collar opening, and windbox means surrounding said end portion of said sleeve and communicating with said first flow passage for receiving air and directing same to said first flow passage for passage to said collar opening, said sleeve having a plurality of openings extending therethrough for directing air through said second flow passage and through said openings in said base of said insert. for passage to said collar opening.

2. The assembly of claim 1 wherein said burner member is coaxially disposed relative to said sleeve and wherein said flow passages direct air towards the axes of said burner member and said sleeve.

3. The assembly of claim 2 wherein a portion of the wall of said insert and said end portion of said sleeve extend at an angle to said axes to direct air towards said axes.

4. The assembly of claim 1 further comprising means disposed in said first flow passage for swirling air as it discharges to said collar opening.

5. The assembly of claim 1 further comprising regis ter means disposed in said windbox and surrounding said end portion of said sleeve, said register means communicating with said first flow passage for directing air to said first flow passage, and vane means disposed in said register means for varying the flow path of air through said register means and to said first flow passage.

6. The assembly of claim 1 wherein a first burner member extends in a coaxial relationship with said sleeve and a plurality of additional burner members are disposed in a radially spaced relationship to said first burner member and are spaced along a circle.

7. The assembly of claim 6 wherein said first burner member is adapted to discharge a fuel that is different from the fuel discharged by said additional burner members.

8. The assembly of claim I wherein the amount of air passing through the openings in said sleeve is approximately 10% of the total amount of air passed to said collar opening.

9. The assembly of claim 1 wherein the total amount of air passed to said collar opening is less than the theoretical amount required for complete combustion.

Patent No. Dated 29, 1975 Walter P. Gorzegno Inventor (s) It is certified that error appears in the above-identified patent Q and that said Letters Patent are hereby corrected as shown below:

Inventor's name should read Walter P. Gorzegno Signed and Scaled this twenty-seve th D a) f January 1 9 76 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Patents and Trademarks 

1. A burner assembly for mounting adjacent an opening in the wall of a furnace, comprising a collar having one end portion extending in said wall opening, another end portion located externally of said furnace, and a through opening communicating with the interior of said furnace, a sleeve disposed externally of said furnace and having an end portion cooperating with said other end portion of said collar to define a first annular flow passage communicating with said collar opening, a substantially cup-shaped insert disposed in said sleeve with the base of said insert disposed inwardly from said end portion of said sleeve and having a plurality of openings extending therethrough, the wall of said insert cooperating with said end portion of said sleeve to define a second annular flow passage communicating with said collar opening, at least one burner member disposed in said sleeve and adapted to discharge a stream of fuel into said collar opening, and windbox means surrounding said end portion of said sleeve and communicating with said first flow passage for receiving air and directing same to said first flow passage for passage to said collar opening, said sleeve having a plurality of openings extending therethrough for directing air through said second flow passage and through said openings in said base of said insert, for passage to said collar opening.
 2. The assembly of claim 1 wherein said burner member is coaxially disposed relative to said sleeve and wherein said flow passages direct air towards the axes of said burner member and said sleeve.
 3. The assembly of claim 2 wherein a portion of the wall of said insert and said end portion of said sleeve extend at an angle to said axes to direct air towards said axes.
 4. The assembly of claim 1 further comprising means disposed in said first flow passage for swirling air as it discharges to said collar opening.
 5. The assembly of claim 1 further comprising register means disposed in said windbOx and surrounding said end portion of said sleeve, said register means communicating with said first flow passage for directing air to said first flow passage, and vane means disposed in said register means for varying the flow path of air through said register means and to said first flow passage.
 6. The assembly of claim 1 wherein a first burner member extends in a coaxial relationship with said sleeve and a plurality of additional burner members are disposed in a radially spaced relationship to said first burner member and are spaced along a circle.
 7. The assembly of claim 6 wherein said first burner member is adapted to discharge a fuel that is different from the fuel discharged by said additional burner members.
 8. The assembly of claim 1 wherein the amount of air passing through the openings in said sleeve is approximately 10% of the total amount of air passed to said collar opening.
 9. The assembly of claim 1 wherein the total amount of air passed to said collar opening is less than the theoretical amount required for complete combustion. 